Plating apparatus with recovery of plating chemicals from rinse waters

ABSTRACT

In a unit for reclaiming plating wastes containing chromic acid and the like, the rinse liquid from the first of a plurality of wash tubs into which plated articles are dipped successively to rinse off the plating solution, is sucked into a tower where it is heated by steam partially to vaporize and concentrate it to plating strength. The vapor generated in the tower is passed through a check valve to an ejector, where it is introduced transversely into a jet of cooling water to be condensed and conveyed with the stream of cooling water to a reservoir. The cooling-water jet develops a vacuum in the tower; and a trap is interposed between the tower and ejector to trap any cooling water which a faulty check valve might otherwise allow to back up into the tower.

United States Patent [72] Inventor Aisaburo Yagishita 5-2, Shinpo-cho, 4-chome, Chigusa-ku, Nagoya, Japan [21] Appl. No. 66,398 [22] Filed Aug. 24, 1970 Division Of Ser. N0. 587,607, Oct. 18;

h p 1966, Pat. No. 3,542,651 [45] Patented Oct. 26, 1971 [54] PLATING APPARATUS WITH RECOVERY OF PLATING CHEMICALS FROM RINSE WATERS 4 Claims, 3 Drawing Figs.

[52] 0.8. CI 204/232, 159/23, 202/182, 202/185 A, 202/205, 203/1 203ID1G. 16, 204/51, 204/237 [51] I Int. Cl 801k 3/00 [50] Field of Search 159/DIG. 16; 202/182, 185 A, 205, 169, 162;204/51,232, 237

[56] References Cited UNITED STATES PATENTS 52,253 1/1866 Miller 159/23 X 393,488 11/1888 Schutte 159/DIG. 16 585,365 6/1897 Skiffington 202/185 A 1,149,627 8/1915 Bunnell 159/23 X 2,853,442 9/1958 Swanton 204/28 OTHER REFERENCES D. Gardner Foulke, Plating, vol. 53, no. 10, pp. 1217- 1221, (1966) A. K. et al., Plating Vol.53, No. 10, pp. 1222- 1229 (1966).

Primary ExaminerG. L. Kaplan Attorney-Shlesinger, Fitzsimmons & Shlesinger I tower is passed through a check valve to an ejector, where it is introduced transversely into a jet of cooling water to be condensed and conveyed with the stream of cooling water to a reservoir. The cooling-water jet develops a vacuum in the tower; and a trap is interposed between the tower and ejector to trap any coolingwater which a faulty check valve might otherwise allow to back up into the tower.

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PLATING APPARATUS WITH RECOVERY OF PLATING CHEMICALS FROM RINSE WATERS This application is a division of my copending U.S. Pat. application, Ser. No. 587,607, filed Oct. 18, 1966, now U.S. Pat. No. 3,542,651.

This invention relates to a unit for disposal of plant wastes. More particularly, this invention relates to a unit for recovery of wastes from metal-finishing plants, such as plating wastes containing chromic acid and the like.

In a number of industries involving the operation of rinsing the products from chemical treatment processes, the amount of effective chemicals in the rinse liquid is considerable, and recovery of such chemicals has had great economical significance. Moreover, such rinse liquid as a caustic soda solution from a mercerizing process in the fiber industry or a plating solution in the plating industry would result in considerable pollution of streams if they were discharged from rinsing operations following mercerizing or plating operations. Thus, the recovery of such chemicals has been regarded as a necessity from the standpoint of conservation of stream water quality.

In general, the kind of chemicals in the rinse liquids varies from one rinsing operation to another. Most of these liquids are appreciably diluted solutions as compared with the original plating solution, and recovery of chemicals in the rinse liquid is a matter of difficulty because of the expense involved. In a minority of cases, recovery of the expensive chemicals is planned, however, the bulk of such chemicals are discharged from rinsing operations following chemical treatment processes; and a recovery unit that might work out in a most economical and simplified manner has been in demand.

Hence, an object of the present invention is to provide a unit which attains recovery of chemicals contained in a rinse liquid in an economical and simplified manner by rationalizing the usage of rinse liquid either through collecting highly contaminated liquid and returning the same to the operating tank, such as a plating tank, or transferring the liquid to a heating and concentrating tower for concentration, depending on the concentration or level of the liquid contained in the operating tank.

Another object of the present invention is to provide a recovery unit wherein waste water containing toxic chemicals is not discharged from the plant and savings of effluent water may be attained.

A further object of the present invention is to provide a recovery unit having a novel condenser in which cooling water passing through an ejector is entrained in the vapor stream from a heating and concentrating tower fitted to a plant-waste recovery unit, and the vapor is condensed through cooling by cooling water, and wherein means is provided to prevent backflow of such cooling water into said heating and concentrating tower via the route of exhaust vapor and thereby avoiding resultant dilution of the concentration of the liquid contained in the tower.

Now, the present invention will be described hereinbelow with reference to certain embodiments thereof as illustrated in the accompanying drawing, in which:

FIG. I is an explanatory view showing partly in section and I partly in full a recovery unit made in accordance with one embodiment of the present invention;

FIG. 2 is an enlarged fragmentary sectional view showing in elevation a preferred embodiment of a condenser employed in this recovery unit; and

FIG. 3 is a wiring diagram illustrating one manner in which the electrical components which form part of this condenser may be wired for operation.

Referring first to FIG. 1, by way of giving a detailed explanation of the unit according to the present invention, a plurality of wash water tubs 2, 3, 4, 5 are connected in series with the plating tank 1, the fourth tub 2 among the wash water tubs serving as the hot wash water tub.

The wash water tubs 2, 3, 4, 5 are connected one with the other by means of siphons 15, 16 and 17, and the fourth tub 2 is fitted with an overflow pipe 14. To the first wash water tub 5 is connected a heating and concentrating tower 7 via a feed pipe 6. Heating of the liquid to be concentrated is effected by means of the steam sent forth into the heating unit 12 enclosed inside said tower via pipe 18- and waste steam is exhausted via pipe 19. Furthermore, a condenser unit 10 is annexed'to the heating and concentrating tower 7 to condense the vapor evaporated from the tub water supplied into said tower and heated by the heating steam. Cooling water is passed through helically wound cooling pipe 11 inserted into said unit 10 and the hot water heat exchanged in the condenser unit 10 is passed through said cooling pipe 11 and is supplied to the fourth wash water tub or hot wash water tub 2. Tub water in the first wash water tub 5 pumped into the heating and concentrating tower 7 via feed pipe 6 is heated and concentrated to the level equivalent to that of the plating solution contained in the plating tank 1 before it is restored 'to the plating tank via pipe 8. Water is supplied at times to the warm wash water tub 2 via pipe 13.

Supposing that plating operation comprising moving the plated ware from the plating tank and immersing the same consecutively in a series of wash water tubs is conducted in a chromium-plating plant employing 10 kg. of chromic acid per 8 hours a day, and that the capacity of the first wash water tub 5 is 200 liters, the metallic articles plated in the plating tank I are washed consecutively in the wash water tubs 5, 4 and 3 and finally in the hot water tub 2. If the recovery un'it according to the present invention is not utilized, approximately percent of chromic acid contained in the plating tank 1 goes onto the plated ware and carried off the plating tank I, and the chromic acid concentration levels of the wash water tubs 5, 4, 3 when the operation is finished are approximately 45 g./I., 6.5 g./l. and 0.6 g./l. respectively.

On the other hand, if the recovery unit according to the present invention is utilized, supposing that the evaporative capacity of the heating and concentrating tower 7 is l 00 kg./h. and that the capacity of the first wash water tub 5 is 200 liters and other conditions are also same as above, the tub water contained in the tub 5 is diminished by one-half per hour, and the tub 5 is supplied with wash water from the second, third and fourth wash water tubs by means of siphons l5, l6, 17. The wash water contained in the wash water tubs 5, 4, 3 is diluted and chromic acid concentration levels of the tubs 5, 4, 3 are maintained respectively at l5 g./l., l g./l. and 0.08 g./l., or thereabout.

As will be seen from the above, the concentration levels of the second and third wash water tubs 4, 3 are so low that,

.needless to say, concentration of wash water contained in these tubs cannot be attained on an economical basis.

Referring now to the embodiment of condenser illustrated in FIGS. 2 and 3, wherein like numerals are employed to denote elements similar to those of the unit illustrated in FIG. l, the heating device 12 is disposed within the tower 7, and the liquid stored in the tower for concentration is heated and evaporated by the steam supplied from piping 18. The evaporated vapor passes through a device 33, which prevents undesireable sprayings through pipe 9, swings open the swing valve 41 of the check valve 40, and reaches an ejector 42. Cooling water from a reservoir 43 is pumped into the ejector 42 via pipe 45 by means of a pump 44, and is entrained in the vapor stream coming from the heating and concentrating tower 7, whereby the vapor is cooled and condensed, 'and together with the cooling water is exhausted to the hotwell 46 and discharged. Vacuum is maintained in the heating and concentrating tower 7 due to suction of vapor effected by the ejector 42 to lower the boiling point of the liquid to be concentrated and to promote its evaporation.

In actual operation of the above-mentioned device, the degree of vacuum in the heating and concentrating tower 7 is not always constant and, moreover, the supply of heating steam to the heating device 12 varies from time to time. So. the liquid to be concentrated is boiled and vaporized intermit tently, and the exhaust vapor from pipe 9 causes vibration of the swing valve 41. In addition, cooling water pumped by the pump 44 into the ejector 42 collides with the vapor which is supplied intermittently, with the result that the temperature of the cooling water is elevated and lowered cyclically, and the performance of the ejector 42 fluctuates. This causes further vibration of the swing valve 41 to the point where the check valve 40 may be rendered inoperative and may thus permit the cooling water to flow in pipe 9 to the concentrating tower 7, which normally is under vacuum or reduced pressure compared to the cooling water, thus, to dilute the liquid in the tower.

It is apparent that the possibility of undesireable reversal of cooling water from the ejector 42 to the tower 7 would be increased in the case of a vacuum heating and concentrating device without the provision of a properly operating check valve 40.

In order to overcome such deficiency, a trap 48 consisting of a hermetically sealed vessel is connected by a perpendicular branch pipe 47 to the midportion of the pipe 9, which connects the concentrating tower 7 and the ejector 42 in a closed loop. ln this way, cooling water reversed from the ejector 42 via pipe 9 may enter pipe 47 to be stored inside the trap 48, thereby being prevented from entering the concentrating tower 7.

A liquid-level detector 50 is placed in the trap 48 so as to control the operation of the liquid-level controller 51 (FIG. 3). Such liquid-level detector 50 may consist of a pair of electrodes which may be connected electrically by the cooling water stored in the trap 48, when the water reaches a certain level, and the ends of the electrodes are thus immersed in the water. In the arrangement above-described, when the cooling water in the trap 48 has risen to a certain level, the pump 44 is stopped automatically and does not come into operation until the valve or drain cock 49 of the trap 48 is opened to exhaust collected cooling water.

H6. 3 shows an example of a simple electrical wiring of this kind of trap device. In this example, liquid-level controller 51 is a relay and its coil is serially connected in the control circuit 52 with the two electrodes of the liquid-level detector 50, while a normally closed switch 55 controlled by this relay is inserted in the circuit 53 for driving the pump 44, and in series with a manually operable on-off switch 54. When switch 54 is closed, the pump 44 will operate until the liquid rises far enough in tank 48 to engage the two electrodes ofdetector 50. This closes circuit 52 and energizes the relay coil of controller 51 thereby opening switch 55 to stop the operation of pump 44.

Having thus described my invention, what I claim is:

1. in a unit for recovery of wastes from metal-finishing plants, and having a plating tank, a plurality of wash tubs into which plated articles are dipped successively to rinse plating solution therefrom, and a heating and concentrating tower for heating and vaporizing wash water from one of said tubs to concentrate said water to plating strength for return to said plating tank, a condenser unit comprising a first pipe connected at one end to a vapor chamber in said tower above the wash water therein,

an ejector connected to the opposite end of said pipe,

means for pumping a jet of cooling water from a supply thereof through said ejector and in a direction to lower the pressure in said ejector relative to said chamber, whereby vapor is drawn from said chamber into contact with said jet of water to be condensed thereby,

a check valve interposed in said first pipe normally to prevent flow of cooling water from said ejector to said chamber, and

means connected to said first pipe between said chamber and said ejector to trap any of said cooling water which flows rearwardly from said ejector through said valve.

2. A unit as defined in claim 1, wherein the last-named means comprises a reservoir positioned beneath said first pipe, and

a second pipe connected at its upper end to said first pipe, and at its lower end to said reservoir, thereby to convey by gravity to said reservoir any of said cooling water which flows rearwardly throuah said check valve. 3. A unit as defined in claim including means in said reservoir for sensing the level of the water therein, and

means connecting said sensing means to said pumping means and operative to interrupt the operation of said pumping means, when said level of the water in said reservoir reaches a predetermined height.

4. A unit as defined in claim 3, wherein said sensing means comprises a pair of spaced members projecting into the top of said reservoir to form a normally open switch,

a relay coil is electrically connected in a first series circuit with said members,

said pumping means comprises a pump having a control circuit connected in parallel with said first-series circuit, and in a second-series circuit with a normally closed switch controlled by said relay coil, and

means is provided for connecting said circuits to a power supply to energize said pump through said normally closed switch, when said coil is deenergized, and to energize said coil to open said switch, when the level of the water in said reservoir has risen high enough to engage said members.

i l i I! i 

2. A unit as defined in claim 1, wherein the last-named means comprises a reservoir positioned beneath said first pipe, and a second pipe connected at its upper end to said first pipe, and at its lower end to said reservoir, thereby to convey by gravity to said reservoir any of said cooling water which flows rearwardly through said check valve.
 3. A unit as defined in claim 2, including means in said reservoir for sensing the level of the water therein, and means connecting said sensing means to said pumping means and operative to interrupt the operation of said pumping means, when said level of the water in said reservoir reaches a predetermined height.
 4. A unit as defined in claim 3, wherein said sensing means comprises a pair of spaced members projecting into the top of said reservoir to form a normally open switch, a relay coil is electrically connected in a first series circuit with said members, said pumping means comprises a pump having a control circuit connected in parallel with said first-series circuit, and in a second-series circuit with a normally closed switch controlled by said relay coil, and means is provided for connecting said circuits to a power supply to energize said pump through said normally closed switch, when said coil is deenergized, and to energize said coil to open said switch, when the level of the water in said reservoir has risen high enough to engage said members. 